This invention relates to an improvement in a light-sensitive silver halide photographic material and, more particularly, it is concerned with a light-sensitive silver halide photographic material which has a high sensitivity and a favorable gradation, shows a superior pressure resistance and stability with the lapse of time as a light-sensitive material and is suitable for a low replenishing type process.
Recently, a high speed developing process for a light-sensitive silver halide photographic material (hereinafter referred to simply as a light-sensitive material) has been carried forward and, moreover, reduction in a volume of a replenishing solution has been increased with concentration of a replenishing developing solution for improved working efficiency and reduced cost; the so-called low replenishing type developing solution has been used. In reply to the trend in this field, there has been much need for a light-sensitive silver halide photographic material having a rapid processibility and a low replenishing type aptitude. However, a halogen ion has been accumulated at a higher concentration in a low replenishing type developing solution, as compared with the prior type developing solution.
In general, a halogen ion has a development retarding effect and an iodine ion shows a particularly strong effect and a bromine ion and a chlorine ion show said effect in order, a retarding power of chlorine ion being very weak in comparison with the other two ions. Therefore, studies have been made for meeting the said need by using a silver chlorobromide emulsion having a relatively high chlorine content, but the higher the silver chloride content becomes, the lower is the sensitivity. Further, there has been presented a problem of increased fogging when a light-sensitive material is stored with time. A high sensitizing technique has been required to compensate for said reduced sensitivity.
Also, there has been taught a high sensitization using a mono-dispersed emulsion, among studies on sensitization techniques approached from various aspects.
For instance, there has been reported studies to theoretically calculate quantum efficiency of a silver halide and investigate influence of grain size distribution in a preliminary summary for 1980 Tokyo Symposium about progress of photography, "Interactions between light and materials for photographic applications", page 91. According to this study, it is taught that a mono-dispersed emulsion is effective for improving quantum efficiency, namely, for possible high sensitization. In addition, a mono-dispersed emulsion having a unifor crystal habit and a narrow distribution of grain size is considered to advantageously reach a high sensitivity effectively, while fogging is kept lower, even during chemical sensitization; and thus a light-sensitive material design has been recently attempted using a mono-dispersed emulsion. However, a mono-dispersed emulsion shows too much contrast in gradation because of its property having a very narrow grain size distribution and, particularly, is difficult to be used as a light-sensitive material commonly employed for negative-positive printing.
More specifically, it is desirable for improving such performance as high sensitization etc. to improve mono-dispersability of a silver halide emulsion; but there is an inconsistent relationship, namely, the produced silver halide emulsion, on the other hand, has become more difficult to be applied in regard to gradation, as mono-dispersability has been improved.
For improving this drawback, there has been proposed a method wherein 2 or more sorts of mono-dispersed emulsions are mixed to obtain a favourable gradation, as disclosed, for example, in Japanese Patent Publication No. 56054/1982 and Japanese Provisional Patent Publications No. 58137/1982 and No. 14829/1983. However, it is necessary in this method that 2 or more sorts of different emulsions should be prepared in order to produce one sort of emulsion eventually and step numbers are increased during production, which leads to increase in production cost, so that this method could not be regarded as preferable.
Further, soft gradation has been attempted by reducing an amount of coated silver or coupler for control of gradation; but this method may produce a highly decreased density in a high density portion of image and thus could not form a satisfactory image.
As stated above, a mono-dispersed emulsion composed of silver chlorobromide grains with a relatively high chlorine content may have a high sensitivity, a superior rapid processability and a superior aptitude for a low replenishing type developing solution; but it produces too hard gradation and also has a practically fatal problem of increased fogging from storage of a light-sensitive material with the lapse of time.